This is an implementation of type checking for Ruby.
The implementation is fairly powerful, and allows the
definition of types more or less arbitrarily.  There
is just one tiny problem with this:  I've found it
to only get in the way in practice.

If you want to play with adding extra type checking
to Ruby, I recommend this module.  However, I do
not recommend adding extra type checking (at least
not based on strict checking of method parameters.)

-- Eivind.